This invention relates generally to a magnetic head, particularly a thin film magnetic head, for use in magnetic disks, VTRs (Video Tape Recorders), and so forth. More in particular, the present invention relates to a thin film magnetic head having high performance and high reliability.
A typical conventional thin film magnetic film such as shown in FIG. 2 of the accompanying drawings uses a Ni-Fe alloy film for an upper magnetic pole 19 and a lower magnetic pole 12 which is isolated magnetically from the upper magnetic pole 19, and PIQ (trade name of Hitachi Chemical Co., Ltd.) made of polyimide iosindro-quinazolinedione as a high heat-resistant polymer film material for an insulating layer 21 which electrically isolates both magnetic poles from a coil 16. In this case, PIQ is used as an insulating layer which can withstand the heat when a substrate is heated for forming the Ni-Fe alloy film and can make flat unevenness of the coil. On the other hand, a method of forming a film of the Ni-Fe alloy at a low temperature by a plating method is known. In the thin film magnetic heads of this kind, a photoresist film capable of delicate machining or etching is used as the insulating layer 21 in place of PIQ.
In FIG. 2, reference numerals 11 and 14 represent a substrate and a gap layer, respectively.
The thin film magnetic head using PIQ for the insulating layer is disclosed, for example, in "M. Hanazono et al; J. Appl. Phys., Vol. 53, No. 3, March 1982, pp. 2608-2610". A thin film magnetic head wherein a two-layered coil is covered with PIQ is described, for example, in "Y. Noro et al; J. Appl. Phys., Vol. 53, No. 3, March 1982, pp. 2611-2613".
In order to improve performance of the thin film magnetic head, that is, to improve its S/N ratio, resistance of the coil 16 must be reduced. Accordingly, attempts have been made to increase the sectional area of a conductor. On the other hand, the length of a magnetic path on which the coil is wound is preferably as short as possible. To satisfy these requirements, it has been a customary practice to wind the coil in a multi-layered arrangement. In the thin film magnetic head described above, the coil 16 has the two-layered structure. In this example, the first layer is 9 turns while the second layer is 8 turns to wind a conductor which is 6 .mu.m wide, 3 .mu.m gap and 2 .mu.m high in 17 turns. From the process aspect, however, the number of production steps increases. Therefore, attempts have also been made to wind the coil in a high density and to increase the height by reducing the width and the gap in order to reduce the resistance. If the coil described above is changed from the two-layered structure to the single-layered structure without changing the resistance, for example, the width, gap and height of the coil conductor become approximately 3.about.3.5 .mu.m, 2 .mu.m and 3.5 .mu.m, respectively.
In the thin film magnetic head, an electric and magnetic insulating layer 21 is formed on the coil 16. This insulating layer 21 serves also for making uniform the unevenness due to the coil and for preventing degradation of the characteristics of the upper magnetic pole 19. Both afore-mentioned PIQ and photoresist are employed because they are polymer resins having high fluidity and can easily make flat unevenness due to the coil by spin coating. However, no consideration is made to the method of forming the insulating layer in the case where the coil gap becomes small but its height is great. Therefore, in accordance with the conventional spin coating method alone, bubbles 31 develop between the coil conductors as shown in FIG. 3 and sufficient flatness cannot be obtained easily. Since conventional wirings for a semiconductor device do not require such a wiring having a small gap but a large height, this problem is inherent to the wiring of the thin film magnetic head. Furthermore, unless the upper surface of the insulating layer is made sufficiently flat, the characteristics of the upper magnetic pole formed on the insulating layer get deteriorated. If bubbles occur, they exert adverse influences on flatness and reliability, as well.
Incidentally, reference numeral 32 in FIG. 3 represents an underlying substrate.